1. Field of the Invention
The present invention relates to the field of cleaning a substrate and more particularly to apparatuses and methods for cleaning voids or pores inside a substrate.
2. Discussion of Related Art
Integrated circuits generally are formed by interconnecting devices such as transistors, capacitors, and resistors together with metal lines. The metal lines are typically isolated from each other with dielectric layers. These dielectric layers are sometimes referred to as intermetal dielectric or interlayer dielectrics (ILD). A preferred intermetal dielectric is silicon dioxide (SiO2) which has a dielectric constant of about 4.
The capacitance between two metal layers is given by:   C  =                    ɛ        r            ·              ɛ        0            ·      A        d  wherein d is the distance between the metal layers. The εr value is called a relative dielectric constant (relative to vacuum) or a relative permittivity of a particular dielectric material. The relative permittivity is also called the K value of the dielectric material.
With faster and faster clock frequencies (current microprocessors are made in the MHz and GHz range), the effect of the capacitance between two metal lines becomes more and more important. On top of that the capacitance increases because the distance between two metal lines, d, becomes smaller and smaller with more and more device scaling (e.g., miniaturization). The only way to decrease C is to decrease εr, but since this is a material property, this can only be done by changing the intermetal insulating material. As mentioned above, the conventional intermetal insulating material SiO2 has an εr value of roughly 4. The lowest εr value possible is the value of vacuum, which is 1. Therefore, different intermetal insulating materials are being introduced which have εr values less than 4. A dielectric material having an εr value less than 4 is referred to as low-K material. It is known that air is the best dielectric material but air alone is insufficient to provide the mechanical structure for the electronic devices. FIG. 1 illustrate an exemplary dielectric material 101 having voids or pores 103 to give the low εr value.
Many of the “low-K” materials thus rely on the inclusion of voids or pores to achieve this lowered εr value. Materials with a high degree of voids, or otherwise said porous materials, can have dielectric constant values as low as 2, or half of SiO2.
FIG. 2A illustrates that traditionally, an ILD layer 204 is blanket deposited over a substrate 202 which can be a silicon wafer. Next, a photoresist layer 206 is spun on top of the ILD layer 204 as shown in FIG. 2B. The photoresist layer 206 is then exposed and developed using a patterned mask and UV light as shown in FIG. 2C. Then, a dry dielectric plasma etch is used to etch a pattern in the ILD layer 204 in alignment with the photoresist layer 206 as shown in FIG. 2D. The photoresist layer 206 can be removed with some a dry technique such as a direct plasma strip or a remote plasma strip well practiced in the art. When the photoresist layer 206 is removed, the substrate 202 is left with the ILD layer 204 as shown in FIG. 2E.
After the removal of the photoresist, residues remain on the wafer as well as in the etched features in the intermetallic layer dielectric. These residues must be cleaned before the next step can occur. Most current cleaning techniques for such residues rely on a liquid spraying or immersion step that cleans those residues away. These liquids can be either solvents or aqueous based. When using a liquid to clean residues of a porous material that is being used as a low-K material, the liquid will clean off the residues, but the liquid, because of the capillary force, will be drawn into the pores and voids of the low-K material. FIG. 3 illustrates an example of that a low-k layer 101 formed on a substrate 100 could have liquids trapped within the pores or voids 103. The liquids that are trapped can be water, reagent, or any other rinsing or cleaning liquids that are used to clean the substrate 100 during the making of various electronic devices on the substrate 100.
It is thus advantageous to have methods and apparatuses that can clean low-K materials and that remove liquids from the pores and voids in a cleaned low-K material.